M81 and NGC 3998 are nearby galaxies with mildly active
nuclei, which exhibit LINER-type optical spectra including
broad permitted lines. Their ionization structure suggests
that the nuclear gas is photoionized by a nonstellar nuclear
source, presumably a supermassive black hole. For both
galaxies, we have obtained ground-based and HST/STIS
long-slit spectroscopy, from which we are analyzing the
nuclear stellar dynamics to search for dynamical evidence of
supermassive black holes.

Both galaxies show very high central velocity dispersions
(\sigma of 550 km~s-1 for M81 and 670 km~s-1 for
NGC 3998). After measuring the stellar kinematics from the
data, we have constructed axisymmetric dynamical models
assuming two integrals of motion (orbital energy and angular
momentum). The models for each galaxy point to the presence
of a central dark compact object (presumably a supermassive
black hole) with > 99.5% confidence. The best-fit masses
are 6 \times 107 \ M\odot for M81 and 6 \times 108 \
M\odot for NGC~3998, with internal error of 20% and
10%, respectively. We are refining these measurements by
constructing axisymmetric three integral models utilizing an
orbit-based technique.

Support for this work was provided by NASA through grant
GO-7350 from STScI. Ground-based observations were obtained
from the Michigan Dartmouth MIT Observatory.